Thanks for all the replies, guys! Comments from New Englanders make for very interesting reading.
I've tried to take onboard the comments regarding improvising and have really enjoyed the wild goose chases/strange developing storyline as a result of it.
Last night we went through day four of TTH and it resulted in several interesting points. The group dreams piqued interest in a supposed cellar in the MacIearan House and a spot hidden resulted in them finding a previously hidden trapdoor which contained little apart from rotting farming reference books.
Things went a little wayward stumbled upon the clearing after tracking Jimmy MacIearan (this was the closest that they got to getting back on track), the biologically minded investigator ended up killing and taking the corpse of a zoog before the group narrowly escaped the pursuit of fifty more of the little critters.
While I let things go a little bit crazy, they had a great session that involved some rather exciting moments for the investigators. I did try very hard to get them back on track, they didn't take the bait.
Stinks